1. Field of the Invention
The present invention relates to a radiation image information recording/reading apparatus for recording radiation image information in a stimulable phosphor sheet and for obtaining an image signal representing the radiation image information by photoelectrically reading light emitted from the sheet upon exposure of the sheet to excitation light.
2. Description of the Related Art
Radiation image recording reproducing systems using stimulable phosphor sheets have been widely put into practice. Stimulable phosphor stores a portion of energy of radiation irradiated thereon and emits light in accordance with the stored radiation energy upon exposure to an excitation light such as visible light or a laser beam. A stimulable phosphor sheet includes such stimulable phosphor covering a substrate.
In such a radiation image recording reproducing system, radiation that has passed through a subject such as a human body is irradiated on a stimulable phosphor sheet to record radiation image information of the subject in the sheet. Thereafter, the sheet is scanned two-dimensionally with an excitation light such as a laser beam to cause the sheet to emit light from an area on which the excitation light has been irradiated, and obtains an image signal representing the radiation image information by reading the light with photoelectric reading means (see Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 55(1980)-116340 and 56(1981)-104645, for example).
The image signal obtained by the system is subjected to image processing such as tone processing and frequency processing appropriate for observing an image represented by the image signal. The image is reproduced as a visible image on a film, or displayed on a CRT image display device for diagnosis. The stimulable phosphor sheet after reading the radiation image information can be used repeatedly to store radiation image information if erasing light is irradiated thereon to release residual energy from the sheet.
Furthermore, radiation image information recording/reading apparatus taking advantage of reusability of stimulable phosphor sheets have also been in wide use (see Japanese Unexamined Patent Publication Nos. 59(1984)-192240 and 63(1988)-131134, for example). In such an apparatus, radiation image information is recorded in a stimulable phosphor sheet and read therefrom, the stimulable phosphor sheet being used repeatedly.
Such a radiation image information recording/reading apparatus basically comprises:
an image recording unit for recording radiation image information in a stimulable phosphor sheet by irradiating radiation representing the radiation image information on the sheet;
excitation light main scan means for carrying out main scan of the sheet having the radiation image information therein with excitation light irradiated from a side opposite a side of irradiation of the radiation;
vertical scan means for relatively moving either the sheet or the main scan means to the other in a direction crossing a direction of the main scan;
photoelectric detection means for detecting light emitted from an area in the sheet on which the excitation light has been irradiated, from a side of irradiation of the excitation light and from a side opposite of the excitation light irradiation; and
erasing means for releasing residual radiation energy from the sheet after reading the light, prior to recording of another image in the sheet by the image recording unit.
The stimulable phosphor sheet may be subjected to the radiation image information reading while staying in a position where the radiation image information has been recorded on the sheet (that is, the excitation light irradiation and the detection of the light are carried out at the same position), or may be conveyed by conveyor means to an image reading unit of the apparatus comprising the photoelectric detection means and the like for the radiation image information reading after the radiation image information has been recorded in the sheet.
A sheet having high rigidity and thus practically inflexible may be used as the stimulable phosphor sheet. This stimulable phosphor sheet of so-called rigid type has the advantage that it does not need to be conveyed by sheet conveyor means such as an endless belt and can be moved directly, unlike a stimulable phosphor sheet having flexibility.
In the radiation image information recording/reading apparatus described above, the excitation light irradiation and the detection of the light being performed from a side opposite a side of the radiation irradiation has been proposed for the sake of downsizing of the apparatus, especially in the case where the stimulable phosphor sheet of rigid type is fixed in a photographing position where the sheet is also read for the radiation image information.
However, even if such a configuration is adopted, a conventional radiation image information recording/reading apparatus uses raster scan means for two-dimensional scan of the stimulable phosphor sheet by using a light beam deflected by a light deflector. Furthermore, photomultipliers are used as the photoelectric detection means in the apparatus. Therefore, downsizing has been difficult.